Corrosion inhibitors



United States Patent CORROSION INHIBITORS No Drawing. Filed July 5,1955, Ser. No. 520,167

4'Claims. (Cl. 21-2.5)

This invention relates to inhibiting the corrosion of metals and metalsurfaces and more particularly it relates to corrosion inhibitors whichare effective on a variety of metals and which are easily applied.

There are many pieces of mechanical equipment containing intricate metalparts which are used only intermittently. Engines, including gasoline,diesel, jet etc., farm and marine equipment, machine tools, containers,bins, etc., are illustrative of items which have intermittent periods ofuse. It is desirable to have a rapid and easy method for protectingmetal surfaces forming a part of these items. Since many of them containparts which because of their location or intricacy are inaccessible tothe common methods of applying an anti-corrosion coating (such aspainting, spraying or dipping) it is essential to provide a corrosioninhibitor which may be carried into and around these intricate orinaccessible parts by means of a gas or easily introduced liquid.

The pieces of mechanical equipment to be protected are not onlyintricate in construction but they also are composed of parts made of awide variety of metals, including steel, magnesium, aluminum, bronze,brass and bearing materials. This is particularly true of internalcombustion engines and also of jet engines. It is well known thatcorrosion inhibitors which are basic in character protect steel butattack magnesium and aluminum while those corrosion inhibitors whichcontain nitrous salts of amines protect steel and magnesium and aluminumbut attack copper-containing alloys. Thus, it is desirable to find acorrosion inhibitor which is easily applied and which protects a widevariety of metals and their alloys.

Internal combustion engines and jet motors are very often exposed to seawater spray, atmospheres of exceedingly high humidities, and theordinary products of combination, including those from leaded fuels,which remain in the engine or jet motor after shutdowns. The corrosioninhibitors of this invention are particularly well suited to protectmetal surfaces from these corrosive agents.

There are a number of methods known for protecting metal surfacesagainst moisture and corrosive vapors, but many of them either deposit apermanent coating on the surface or use materials, such as heavy greaseswhich require a great deal of time to remove. The coating deposited bythe corrosion inhibitors of this invention on the other hand, isneitherlpermanent nor does it have to be removed before operations canbe continued.

The use of corrosion inhibitors such as dicyclohexylamine nitrite whichmay be vaporized for more convenient deposition on the metal surface tobe protected is known in the art. However, as pointed out above, suchvaporphase corrosion inhibitors do not protect all types of metals. Infact, it has often been necessary to protect one type of metallicsurface to the detriment of another type or types of metal. A moredesirable corrosion inhibitor would, therefore, be one which can beeasily applied in its vapor state, in solution or in the form of anaerosol-type dispersion and which will be effective in protecting a widerange of metal surfaces without having any adverse effects. This ineffect involves finding a Patented Aug. 2, 1960 corrosion inhibitorwhich is a good compromise in its ability to protect many differentmetal surfaces.

An object of this invention is to furnish a volatilizable inhibitorcapable of protecting a wide variety of metal surfaces including steel,aluminum, magnesium, brass, bronze and bearing metals. Another object isto furnish corrosion inhibitors which may be readily applied and whichdo not require a special operation for their removal. A further objectof this invention is to protect metal surfaces not only againstcorrosion due to contact with air, water and sea spray but also againstthat due to the products of combustion encountered in engines and jetmotors. An additional object is to provide corrosion inhibitors whichare hydrophobic in character. These and other objects will appear in thefollowing discussion.

The improved corrosion inhibitors of this invention are organic sulfidesof the general formula CHM-R where n has the value of one or two and Ris either 0 II C-O-R i O-C-R in which R is an alkyl radical, beingunsubstituted or substituted with hydrocarbon radicals.

It will be noted that the corrosion inhibitors of this invention asdefined by the above formula are neutral compounds and do not have theamino group. Thus, the deleterious effects on aluminum and magnesiumcaused by alkaline compounds and the adverse effects of the amino groupon copper and copper-containing metals are all eliminated.

The sulfide linkage of these corrosion inhibitors may be introducedeither by way of the alcohol or by way of the acid as indicated in thetwo possible general forms for R. The preparation of typicalrepresentatives of this class of compounds may be found in J. Chem. Soc.1950, 3061 (1950), for thiodiglycol diacetate; J. Am. Chem. Soc. 69, 241(1947) for di-(2-ethylhexyl)thiodipropionate; and Berichte 63, 2393(1930) and Fihnel and Carmack Organic Syntheses, vol. 30, p. 65 (1950),for dimethyl thiodipropionate.

The esters of thiodiacetic acid and of 3,3'-thiodipropionic acid, andmore particularly di-(2-ethylhexyl)thiodipropionate anddi-(Z-ethylhexyl)thiodiacetate, have been found to be especiallyeffective in preventing corrosion in internal combustion engines and jetmotors.

The mechanism of corrosion inhibition is not too well understood but itis generally assumed that the inhibiting agent or its vapor reacts with,or is somehow attracted to, the exposed surface molecules of the metalto be protected.

In the case of the esters of this invention it appears that two effects,both contributing to the protection of the metal, are present. The firstof these is the effect of the S (sulfide) linkage, while the secondappears to be an effect of the remaining portion of the molecule. Areasonable explanation would seem to be that the S linkage reacts or isin some manner attracted to the surface molecules of the metal to beprotected to form a surface coating which is less reactive with thecorroding agents such as water vapor, combustion gases and sea spray.

The fact that a compound such as an alkyl mercaptan containing thesulfide linkage, but not two alkyl chains, does not prevent corrosion(see Bul. soc. chim. 1954,

650 (1954)), is strong indication that the additional alkyl radical alsocontributes to the overall corrosion inhibiting efiect. One possibleexplanation is that the alkyl radical gives the corrosion inhibitors ofthis invention a paraifinic character and hence accounts for thehydrophobic character which they exhibit on the protected metalsurfaces. Such a hydrophobic character is particularly important forcorrosion inhibitors designed to protect metal surfaces from atmospheresof very high humidities.

A bench test was devised to test the effectiveness of the corrosioninhibitors of this invention and to compare them with corrosioninhibitors now in use. In this bench test the metal specimen, supportedfrom the top of a 250-ml. wide' mouth Erlenmeyer flask by a nylonthread, was exposed to water vapor and the inhibitor in the flask. Thesetests were run at room temperature and at 150 F. The polished sampleswere graded on the basis of zero to four, where zero represented nocorrosion and four represented complete! attack on the specimen surface.

Typical results from these bench tests are given in Table I.

TABLE I from the vapor phase as is conventionally done for vapor-phasecorrosion inhibition, other means of application are equally wellsuited. Such other means include, but are not limited to, brushing orspraying on solutions made up with acetone or other suitable solvents,suspending finely divided particles in the form of an aerosol (i.e., asa coloidial system in a gas), or

engine or motor when it is shut down.

entraining them in a current of hot air. In addition, since thecorrosion inhibitors of this invention are soluble in lubricating oilsthey may be dissolved in them and taken into an engine in the oil runthrough the Methods of application which involve vaporization orcarrying finely divided particles in air or as aerosols are alsosuitable for applying the corrosion inhibitors to the internal parts ofengines and jets. If it is desirable to protect small individual partsthe corrosion inhibitors may be used to treat wrapping paper (as byimpregnation followed by drying) Which in turn may be used to wrap aboutthe parts or to be put in a closed container along with the metalsurfaces to be protected.

I claim:

1. Process for inhibiting the corrosion of the internal Effectiveness ofcorrosion inhibitors used on different metals found in an internalcombustion engine Hours Lead- Bronze Bronze Al Al Steel CorrosionInhibitor run Indium Bushing Valve Piston Pump Cylinder Average BearingGuide Housing None 85 1 5 0.5 1.5 2.0 0.5 4,0 1.8

Dicyclohexylamine nitrite 89 3 5 0. 0 1.0 1. 0 1. 4 Di-(Z-ethylhexyl)thiodiproplonate 139 0 0 1.5 0.0 0.5 0.5 0.5 0.5

Thiodiglycol diaeetate 41 0 0 2.0 1. 5 0. 5 0.0 3.0 1. l

1 Typical commercial inhibitor.

NOTEs-Gifidtid on basis of 0 to 4. 0=no corrosion; =complete attack onsurface.

Another series of tests were run in which the metal sample was firstexposed to the vaporized inhibitor and then sprayed with a fine mist ofsea water and subsequently stored for 65 hours over sea water in aclosed container so that the sample was in an atmosphere of 100%relative humidity. This meant that there was substantially noevaporization of the sea water on the specimen. Such conditions aresufficient to attack stainless steel. The results of these tests areshown in Table II.

TABLE II Efiectiveness of corrosion inhibitors used on steel, aluminumand magnesium Aluminum Stainless Average Steel Corrosion InhibitorMagneslum None Dicyciohexylamine nitrite (proprietary composition) Di (2ethylhexyl) th to dipropionate Di-t(2-ethylhexyl) thio diaceta eDimethyl thiodipropionate Di-isopropyl thiodipropionate Thiodiglycoldiacetate parts of an engine which comprises introducing a corrosioninhibitor as a vapor into the engine intake, said corrosion inhibitorcomprising a compound of the general formula l)nR' s where n is aninteger selected from one and two and R is a radical selected from thegroup consisting of and wherein R is an alkyl radical having from one toeight carbon atoms.

2. An anti-corrosion wrapping paper suitable for protecting metallicobjects, said wrapping paper being impregnated with a corrosioninhibitor, said corrosion inhibitor comprising a compound of the formulawhere n is an integer selected from one and two and R is a radicalselected from the group consisting of wherein R is an alkyl radicalhaving from one to eight carbon atoms.

3. Process for inhibiting the corrosion of a metal surface normallycorrodible by high humidities which comprises at least partiallyenclosing said metal surface in a wrapping paper impregnated with acorrosion-inhibiting amount of a corrosion inhibitor, said corrosioninhibitor comprising a compound of the formula where n is an integerselected from one and two and R' is a radical selected from the groupconsisting of wherein R is an alkyl radical having from one to eightcarbon atoms.

4. The combination comprising a metal article nornormally corrodible byhigh humidities and a wrapping paper at least partially enclosing saidmetal article, said wrapping paper impregnated with acorrosion-inhibiting amount of a corrosion inhibitor, said corrosioninhibitor comprising a compound of the formula where n is an integerselected from one and two and R is a radical selected from the groupconsisting of References Cited in the file of this patent UNITED STATESPATENTS 2,262,686 Kyrides Nov. 11, 1941 2,331,270 George Oct. 5, 19432,475,186 Kamlet July 5, 1949 2,481,372 Fuchs Sept. 6, 1949 2,649,416Richter et a1 Aug. 18, 1953 2,653,854 Schaar Sept. 29, 1953 2,717,196Wachter Sept. 6, 195.5

2. AN ANTI-CORROSION WRAPPING PAPER SUITABLE FOR PROTECTING METALLICOBJECTS, SAID WRAPPING PAPER BEING IMPREGNATED WITH A CORROSIONINHIBITOR, SAID CORROSION INHIBITOR COMPRISING A COMPOUND OF THE FORMULA